Thermosetting protective coatings are widely used in original equipment manufacturer (OEM) and industrial maintenance fields. Thermosetting acrylics are known to exhibit excellent light stability and hydrolysis resistance in general. There is broad latitude in terms of property adjustment with acrylics that can be fine tuned to fit many particular applications. Acrylics have the capability to provide many desirable characteristics such as increased hardness; fast dry time; stain resistance and excellent outdoor durability. Consequently, thermosetting acrylics are used as primary film-forming resins in coatings for transportation, industrial maintenance, and marine coatings.
Although thermosetting acrylics exhibit many desirable properties, they often lack flexibility and chemical resistance. These are crucial properties required in many applications including coil coatings, train/container and other coatings. Thermosetting polyesters are the primary film-forming resins in these fields due to their excellent flexibility and chemical resistance as compared to thermosetting acrylics. Thermosetting polyesters are also know to have a relatively lower viscosity and can produce lower VOC coatings. One shortfall with polyester resins is their hydrolytic stability. Because ester linkages in the polyester backbone are susceptible to attack by water molecules, polyester based coatings are not suitable for objects that are often exposed to high humidity or that come into contact with water. Hydrolytic stability also plays an important role in the durability of the coatings.
Accordingly, it is desirable to have a polymer coating material that is hydrolytically stable and possesses excellent flexibility and chemical resistance.
This invention describes a thermosetting coating composition comprised of at least an aliphatic polycarbonate resin and a cross linker. The aliphatic polycarbonate resins described in this invention are derived from hydroxyl containing compounds including 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) and 1,4-cyclohexane dimethanol (CHDM). The coatings made of these polycarbonates exhibit exceptional toughness. They possess a high degree of hardness while maintaining a high level of flexibility/impact resistance. These polycarbonates resins also exhibited better hydrolytic stability as compared to their polyester counterparts.